The present invention relates to the incorporation of the soluble or sparingly soluble compounds of various elements recognized as essential to plant health and growth in a modified thermoplastic dispensing pellet, powder, granule, or other convenient dispensing form. Such compounds are salts or oxides of well recognized trace elements vital to plant nutrition. Said salts or oxides upon contact with water release zinc, iron, copper, boron, manganese, molybdenum, magnesium, cobalt and selenium in an ionic form as a water solution. Said plants, through natural processes, absorb the trace nutrient during uptake of the nutrient enriched water. Release, being largely moisture dependent, is self-regulatory. During the growing season, wherein soil moisture is readily available, trace nutrient release is continuous and uniform. When moisture is not present, the plants generally do not grow and said nutrients are not released, thus avoiding loss of nutrient.
Heretofore, agronomists and nutritionists have recognized the vital and essential function of various elements needed in minute quantities by growing plants. Such elements have been termed "trace nutrients." Their functions vary, some being essential to the photosynthetic process or being a critical component in various enzyme systems. In general, the complete lack of a given trace element precludes plant growth. For instance, Western Australia would not support agricultural field crops prior to the introduction of zinc into the soil. In most instances where trace nutrients are utilized, the normal soil content is too low for proper nutrition and plants cultivated in said soils are generally more susceptible to disease, show poor growth characteristics and consequently crop yields are low.
It is common practice to supplement trace element poor soils by adding the needful material directly or as an additive in bulk nutrient applications containing those substances classified as "fertilizers", i.e., nitrogen, potassium and phosphorus. Most agricultural commodities require trace element soil supplement for optimum growth and thus maximum yield. Such agricultural commodities include field crops such as wheat, alfalfa, potatoes, clover, tobacco, pineapple, soy beans, sugar, beets, cotton, corn, barley, oats, rice, and the like; citrus fruits; nuts, such as pecans peanuts, coffee, cocoa, walnut, almond; fruits such as apples, pears, cherries, plums, peaches; vegetables, such as beans, peas, cauliflower, carrots, lettuce, tomatoes, cabbage, and the like; and, forestry commodities such as pine trees, and pasture grasses. In the latter case, elements essential to animal growth such as zinc, iron, copper and selenium are ingested by domestic animals consuming said pasture grasses as forage. Lack of trace amounts of critical elements in the cow, sheep, goat and swine lead to deficiency diseases and thus decreased output of meat, milk and wool.
It is probable that lack of application of trace nutrients in U.S. agricultural activities could lead to substantial declines in food production. It is also likely that proper use of trace elements in soils lacking adequate quantities of said materials, such as in vast reaches of Africa, would lead to a dramatic increase in agricultural productivity.
Heretofore, in a typical utilization system, relatively high dosages of trace nutrients are added periodically to the soil. A number of disadvantages, ameliorated by this invention, occur. Said nutrients are of necessity water soluble salts or oxides else the treated plant cannot absorb them. Being water soluble, a large proportion of material applied, perhaps 80 percent or more, is lost from the root zone via natural processes such as percolation in the vertical direction to earth strata below the effective range of the root structure or washed beyond said root range through the movement of ground waters in the horizontal direction. In addition, the type of soil plays a profound role in the trace nutrient contact and ingestion processes. Alkaline soils and/or clay type soils generally complex the added nutrient chemical thus creating insoluble ligands of no value to the nutrient deficient plant. The rate of soil intervention in the nutrition process varies with pH and type, but is an extremely important negative factor.
Relatively massive amounts of the trace elements must thus be applied to overcome natural loss processes and mechanisms. This leads to two distinct and severe disadvantages. In general, treatment must be afforded before such growing season and sometimes followed by one or more retreatments during that season. It is unusual for one treatment to last over any great length of time and consequently, effort is expended and chemicals are purchased repeatedly by the agriculturist at frequent intervals with a concommitant economic factor increasing the cost of foodstuff production. Probably of even greater significance is that massive treatment early in the season leads to luxurious consumption (i.e., consumption beyond real plant needs) early in the growing season with rapidly depleting chemical availability during the middle and late growing season. It is generally recognized that the uniform availability of the trace nutrient in appropriate day-by-day quantities optimizes yield.
The use of controlled-release trace nutrients of the present invention will overcome the luxury consumption, inadequate consumption cycle thus giving greater crop yield, will reduce the total amount of trace nutrient needed, and will also greatly extend between treatment times, from one to two, three, or more years, possibly five or ten years, depending on agricultural practices and natural circumstances (crop rotation and so on).
It is well known that biocidal materials can be incorporated in a polymeric matrix and caused to release at a rate efficacious with pest destruction. U.S. Pat. No. 3,417,181 teaches that organotin toxicants can be dissolved in an elastomer-type matrix and caused to release through a diffusion-dissolution mechanism when exposed to water. The crux of this seminal invention was keyed to the necessity of the agent being soluble in the polymer. Similarly, U.S. Pat. Nos. 3,590,119; 3,426,473; 3,851,053; and 3,639,583 extend the scope of the art to embrace new formulations encompassing different elastomers, specific release regulants that effect the diffusion path length and the like, but again the key concept is the necessity of agent solubility in the elastomer. Agents incorporated are organic pesticides and the generic matrix type is elastomers such as natural rubber, styrene-butadiene rubber, and the like. In contrast, U.S. Pat. No. 4,012,221 teaches that inorganic copper salts capable of being released into water are incorporated in a moderately crosslinked elastomer in which the copper salts are insoluble.
It is well known to the compounding art that agents not soluble within a polymeric matrix will not move at an efficacious rate through said matrix to said matrix surface and thus enter the ambient environment.
Almost all organic pesticidal agents lack solubility in thermoplastic matrixes. Similarly, inorganic pesticidal agents are likewise insoluble in known thermoplastic or thermosetting polymers.
One method of causing an insoluble organic agent to emit from a plastic dispensing unit is to use a third phase material that is (1) soluble in some extent in said plastic and (2) will carry said organic agent in solution or serve as a migratory pathway for said agent to reach the surface of said dispenser. It is, of course, recognized that the incorporated agent must reach the plastic/external environment interface to have any effect on organisms inhibiting the external environment. U.S. Pat. Nos. 2,956,073 and 3,116,201 describe the use of plasticizers as carrier elements. In an improvement on such patents, U.S. Pat. Nos. 3,705,938 and 3,864,468 teach that surface loss from a plasticized matrix is subject to control through the use of a regulating membrane at said surface.
The controlled-release art has been generally confined to the incorporation and release of insecticides, bactericides, molluscicides and other toxic materials of an organic nature from an elastomer, wherein solubility is essential or a plastic, wherein an additive carrier material is critical. Microencapsulation processes wherein an inner core of the toxic agent is surrounded by a polymeric matrix is well known to the pest control art. In general, release is effected by the rupture of the enveloping membrane and/or the passage of water through the porous membrane structure, said water path serving as a means of egress for said pesticide which reaches in this manner the external environment.
Little work has been hitherto performed in the development of efficacious long lasting fertilizing systems. U.S. Pat. No. 3,748,115 teaches that plant nutrients can be bound in a matrix of synthetic rubber, waxes, asphalt, and the like. In this work, four critical elements of the invention are set forth. The fertilizer, emphasizing bulk materials and not trace nutrient, must be uniformly dispensed in a hydrophobic binding element. The dispensing unit must be cylindrical in shape. Said cylinder must be partially coated with a water-insoluble, water-permeable exterior membrane. A portion of the cylinder must be non-coated with said membrane. U.S. Patent 3,520,651 extends this art to teach that more than one nutrient can be incorporated in similar dispensing commodities.
In contrast, the subject invention is related to trace nutrient elements, the binding matrix need not be hydrophobic, the dispenser can take any shape although the granule or pellet is preferred, and no exterior membrane is utilized.
Of course, fertilizing materials have long been compounded with various binders to facilitate dispersal and, in some cases, to prolong availability by slowing the rate of solution in water through precluding immediate nutrient element contact with water. U.S. Pat. No. 3,336,129 teaches that the use of small amounts of water insoluble copolymers and terpolymers of ethers, substituted ethers, ethylene oxide and the like will serve as carriers for fertilizing materials, said copolymers and terpolymers must be crosslinked. Materials are comprised of polymer+fertilizer+water+soil components and the plant is grown within this medium.
Also, fertilizers such as urea can be coated in a granular form as taught in U.S. Pat. No. 3,336,155 thus retarding solution in ground waters. U.S. Pat. No. 3,276,857 teaches that a fertilizer can be encapsulated with asphalt or various waxes and thus emission into the environment is slowed.